I use Chevron's Techcron but regardless of brand, they all do "clean" somewhat but at the dilution level of the average fuel tank, its not gonna do miracles. They help with fuel varnishes and some minor carbon buildup if used regularly but using a good grade of detergent gasoline will do the same. I keep the Chevron stuff around for when I have to use some cut-rate fuel when there is nothing better around. I feel that's where those types of additives really shine. Stopping the crud BEFORE it deposits all thru your fuel system.
Just my $0.02 worth. I'm sure someone will disagree and blast away...:-)